SOC Development at Forschungszentrum Jülich

Abstract

In order to become a substantial part of the energy supply infrastructure in the course of the German “Energiewende” (energy system transition), SOFC plants in the power range of 100 kW or larger must be realized. Scale up of units will become even more important in the field of electrolysis to balance electricity conversion and consumption. Therefore, currently one of the main goals of SOC development at the Forschungszentrum Jülich is the development of single stacks in the 15 kW power range as a basis for development of larger units. The core structural feature is a planar-type window frame stack-design, which allows the integration of standard-sized cells, e.g., 10 ×10 cm², in a 2 × 2 array. Based on this design, the 15 kW stack will consist of six sub-stacks, each having 20 planes. Initial operational results with such a sub-stack are reported. Aiming towards stationary applications, long term behaviour is of great importance. The 'world-record' short stack is now in operation under load for more than 80,000 hours, showing an average voltage degradation rate of 0.6%/kh, which decreased to less than 0.3%/kh in the last 30,000 hours. Next to long term stability, electrical net efficiency plays an important role. A net efficiency of 57% could be demonstrated with a 5 kW system operated with methane at 93% fuel utilization using low temperature anode off-gas recirculation. For stationary applications, a concept was developed and proven that allows safe system operation without additional forming gas.In the case of mobile applications such as range extenders or APUs in trucks, the dynamic behaviour is of greater importance. Therefore, the Jülich lightweight cassette design has been advanced with the potential of improved thermomechanical properties using glass sealing instead of metal soldering to integrate the cells into the cassette frame.Growing emphasis is placed on the development of high temperature electrolysers (SOEC). Currently, a standard two-layer short stack is in operation for more than 18,000 hours in electrolysis mode at a current density of -0.5 A.cm-², showing a voltage degradation of less than 1%/kh. Since in the field of energy storage and electricity production based on renewable energy, the reversible operation of such systems is of great interest, the concept of a 5 kW r(eversible)SOC plant has been devised and is now under construction. A 5 kW stack in a system configuration, representing the fuel cell part of the rSOC system, was operated successfully with a hydrogen utilization of 80%.